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Frequently
Asked Questions |
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2. What types of Radiological
accident are there? 3. Why does Radiological
accident occur? 4. Where does Radiological accident occur? 5. What could be consequences of
Radiological accident? 6. Can the causes of Radiological accident be
influenced by human behavior? 7. Can the consequences of Radiological
accident be influenced by human behavior? 8. Can Radiological accident
be predicted? 9. Is
there any way to prevent Radiological accident? 10.
Is there any way to mitigate
Radiological accident consequences? |
What
is Radiological Accident?
Humans are primarily exposed to natural radiation from the sun, cosmic
rays, and naturally occurring radioactive elements found in the rocks, food,
and environment. Radon, which emanates from the ground, is another
important source of natural radiation. Cosmic rays from space include
energetic protons, electrons, gamma rays, and x rays. The primary radioactive
elements found in the earth's crust are uranium, thorium, and potassium, and
their radioactive derivatives. These elements emit alpha and beta particles,
or gamma rays. The average doses of population exposure due to all nuclear industry
and man-made radioactive sources is about 1% from doses due to natural
radiation, but it is not the case of nuclear or radiological accident. Nuclear or Radiological Accident –
generally refers to events involving the release of significant levels of
radioactivity and exposure of workers or the general public to radiation. What
types of Radiological Accident are there?
A Nuclear Accident is one involving a device that uses a controlled
chain reaction for some purpose. For example,
a Nuclear Power Plant has nuclear fuel that through a self-sustaining and
controlled chain reaction produces heat, turns turbines and produces
electricity. Because of the energy
involved in this process, there is potential for considerable radioactive
material to be released and dispersed into the environment. Such a release would be due to a ‘nuclear
accident’. Normally nuclear accidents with releases to the
environment are very rare. However
they have the potential to lead to widespread dispersion of radioactive
material. Radiological
accidents are initiating by the lost radiation
sources,
accidents during transportation of radioactive sources or materials,
equipment or human errors in radiation sources operation. Sources, often called "sealed sources," are usually small metal
containers in which a small amount of a radioactive material is sealed. Why does
Radiological Accident occur?
The nuclear (power, military or research) reactors are the main
sources of radiation. The radioactivity of nuclear reactor core in millions
times higher, than any other man-made sources of
radiation. Although
construction and operation of nuclear power plants are closely monitored and
regulated, an accident, though unlikely, is possible. The potential danger
from an accident at a nuclear reactor is exposure to radiation. This exposure
could come from the release of radioactive material from the plant into the
environment, usually characterized by a plume (cloud-like) formation. The
size of the area affected is determined by the amount of radioactive material
released from the plant, wind direction and speed, and weather conditions
(i.e., rain, snow, etc.), which would quickly drive the radioactive material
to the ground, causing increased deposition of radionuclides.
Significant contamination could affect areas up to Radiological accidents can occur wherever
radioactive materials are used, stored, or transported. In addition to
nuclear power plants, hospitals, universities, research laboratories,
industries, major highways, railroads, and shipping yards could be the site
of a radiological accident. The radioactive sources are frequently used in
industrial gauges (e.g., moisture and density gauges). If these gauges or
other radiation-containing equipment is disposed of improperly or sent for
recycling as scrap metal, the sealed source may be 'lost' and end up in a
metal recycling facility or in the possession of someone who is not licensed
to handle the source. They are one of the most frequently reported
radioactive contaminants in shipments received by scrap metal facilities. If
a steel mill melts a source, it contaminates the entire batch of metal, the
processing equipment, and the facility. More importantly, it can result in
the exposure of workers or users to radiation. There have also been incidents in which unsuspecting people find these
sources, and not knowing what they are, keep them or even open them and
suffer serious exposures. Some satellites use radioactive materials as a
power source during long space flights. During the launch or re-entry of
satellites there is the potential for an accident that would disperse
radioactive materials. Where does Radiological Accident occur?
Radiation is used in medicine, military, and industry. Main users
of man-made radiation include: medical facilities such as hospitals and
pharmaceutical facilities; research and teaching institutions; nuclear
reactors and their supporting facilities such as uranium mills and
fuel preparation plants; and facilities involved in nuclear weapons
production as part of their normal operation. More then 400 Nuclear Power
Reactors are in operation around the World (see http://www.wano.org.uk/WANO_Documents/WANO_Map/WANO_Map.pdf). On
26 April 1986, the most serious accident in the history of the nuclear
industry occurred at Unit 4 of the Major
releases of radionuclides from the More than 200,000 square kilometers
of Europe was contaminated with levels of 137Cs above 37 kBq/m2.
Much of this area was within the three most affected countries, Belarus,
Russia and Ukraine. See more http://www.tesec-int.org/Chernobyl.htm The worst commercial accident in the United States
occurred at the Three Mile Island nuclear station in 1979. As a result
of equipment failures and operator error, a valve that was stuck open allowed
coolant water that covered the reactor core to escape from the reactor system
for over two hours. This radioactive water, nearly a million gallons, ended
up on the basement floors of the containment building and auxiliary
buildings. The loss of coolant water in the reactor core continued to the
point that the fuel was no longer submerged in water. Without the cooling provided
by the water, the cladding and some of the fuel pellets melted. Large
quantities of radioactive material were released into the containment
building. Radiological accidents are initiating by the lost radiation sources,
accidents during transportation of radioactive sources or materials,
equipment or human errors in radiation sources operation.
One of the most severe radiological accident take place September 1987, Goiania, Brazil. A radiotherapy unit had been abandoned
in a clinic, which was being demolished. The unit had a source consisted of
1375 curies of cesium-137, sealed within two nested stainless steel
containers to form a 5-cm diameter capsule. Two individuals dismantled the
unit and extracted the source, taking it to the home and opened. On 21
September the source material was removed and distributed among several
people, some of whom spread it on their skin. About 112,800 people were
examined of whom 129 were found to be contaminated, 9 people died. What
could be consequences of Radiological Accident?
The
main negative consequences of nuclear or radiological accidents are following: ·
Consequences for health: deterministic effects and
stochastic effects ·
Psychological ·
Environmental ·
Economic ·
Social Consequences for health.
There are basically two types of physical health effect related to radiation
exposure. The first is called a deterministic effect. These
effects occur relatively soon (within days to weeks) after an exposure to a
high dose at a high dose rate. Essentially
the damage to the tissue from the radiation is so extensive that the body does
not have time to regenerate new tissue, and so the effect becomes visible with
many of the features of a thermal burn,
but usually much deeper and long-lasting. The
second type of health effect that can be caused by radiation is a so-called stochastic effect, such as cancer or hereditary effects in any
future offspring. These types of
effects are characterised by their late
appearance after exposure (several years up to decades), and critically that
their occurrence is not certain. The
radiation may cause some damage to the cells of the body which is not visible
but changes the functioning of those cells.
These changes may manifest themselves at a much later date as a cancer
for example. Notice that we say
‘may’ occur, there is no certainty of occurrence.
For stochastic effects, we find that the chance or probability of an
effect increases the higher the radiation dose.
So at low doses there is a very low chance of cancer developing - at
very high doses, there is a higher chance of cancer.
However it appears that there is no ‘safe’ dose, or dose threshold
below which cancers do not occur. Also
it appears that it is the cumulative dose that influences the chance of cancer
development and not the dose rate (at least not strongly). Nuclear
and radiological accidents have also consequences other than just the direct
physical effects on humans. Psychological
health effects will always accompany a nuclear or radiological accident
whether or not it has resulted in persons receiving significant radiation
exposure. Some protective actions
taken during Chernobyl to reduce the radiological health risks, such as
relocation and resettlement, did more harm than good because of the resulting
psychological health effects brought on by stress and anxiety. When
land, water or air becomes contaminated with radioactive material, there is
concern about the environmental effects.
Normally radiation does not affect the ecosystem unless the levels are
very high, although it can damage individual plants and animals.
More problematic are the impact of countermeasures on the environment -
countermeasures that were taken to protect man.
Moreover when the environment becomes contaminated with radioactive
material no matter whether the levels are very small, there is concern among
the population continuing to live there. Finally
environmental processes, such as wind and rivers can transport radioactive
material from one place to another, which raises further concerns. Any
countermeasures taken to address health or environmental impact will have
associated costs, whether they will be the direct cost of the countermeasure
itself, or the lost economic output from formally productive areas.
Together with health and environmental impact the social
consequences associated with the accident and any countermeasures employed, it
is clear that the consequences are often more than just the direct health
consequences alone. Can the causes of Radiological
Accident be influenced by human behavior?
· To prevent the occurrence of failures or abnormal conditions (including breaches of security) that could lead to such a loss of control; · To prevent the escalation of any such failures or abnormal conditions that do occur; · To prevent the loss of, or the loss of control over, a radioactive source or other source of radiation.
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Can Radiological Accident be predicted?
Ionizing
radiation affects people by depositing energy in body tissue, which can cause
cell damage or cell death. In some cases there may be no effect. In other
cases, the cell may survive but become abnormal, either temporarily or
permanently, or an abnormal cell may become malignant. Large doses of
radiation can cause extensive cellular damage and result in death. With
smaller doses, the person or particular irradiated organ(s) may survive, but
the cells are damaged, increasing the chance of cancer. The extent of the
damage depends upon the total amount of energy absorbed, the time period and
dose rate of exposure, and the particular organ(s) exposed. Ionizing radiation is a source of risk for human, but we have to use it for the benefit of community. Is there any way to prevent Radiological Accident?
Defence in depth is provided by an appropriate combination of: · An effective management system with a strong management commitment to safety and a strong safety culture. · Adequate site selection and the incorporation of good design and engineering features providing safety margins, diversity and redundancy, mainly by the use of: - Design, technology and materials of high quality and reliability; - Control, limiting and protection systems and surveillance features; - An appropriate combination of inherent and engineered safety features. - Comprehensive operational procedures and practices as well as accident management procedures. Is there any way to mitigate Radiological Accident consequences?
Mitigation is the measures
undertaken to limit the adverse impact of Radiological Accident. It based on two
main components:
1) to regain control of the situation; 2) prevent or mitigate consequences at the scene; 3) to prevent the occurrence of deterministic health effects in workers and the public; 4) to render first aid and manage the treatment of radiation injuries; 5) to prevent, to the extent practicable, the occurrence of stochastic health effects in the population; 6) to prevent, to the extent practicable, the occurrence of adverse non-radiological effects on individuals and among the population; 7) to protect, to the extent practicable, the environment and property; and 8) to prepare, to the extent practicable, for the resumption of normal social and economic activity. What to do in case of Radiological Accident?
The strategy to reduce public risk in the case of most severe, reactor core damage accident is: Before
or shortly after release - based on plant conditions ·
Evacuate
or substantial shelter within 3 - ·
Take
thyroid blocking near the plant After
a release ·
Prompt
monitoring to locate areas requiring further protective actions. ·
Restrict
consumption of locally grown food up to ·
Monitoring
to locate where food restrictions and relocation are warranted · minimizing exposure time, · maximizing distance from the radiation source, · shielding yourself from the radiation source. Time is an important factor in limiting exposure to the public and to radiological emergency responders. The shorter the period of time an individual stays in a radiation field, the smaller the dose a person will receive. The maximum time to be spent in the radiation environment is defined as the stay time. The stay time can be calculated using the following equation: What types of maps on Radiological Accident exist?
The
emergency plans for facilities with highest radiological risk (like nuclear
power reactors) defining two types of emergency planning areas: ON-SITE AREA This is the area surrounding the facility
within the security perimeter, fence or other designated property marker. It can also be
the controlled area around a radiography source or contaminated area. It is
the area under the immediate control of the facility or operator. For
transport emergencies or emergencies involving uncontrolled sources or
localized contamination there may not be an on-site area defined at the onset
of the emergency. OFF-SITE AREA This is the area beyond that under the
control of the facility operator or first responders. For facilities with the
potential for emergencies resulting in major off-site releases or exposures,
the level of planning will vary depending on the distance from the facility.
For these facilities, planning three emergency planning zones: Precautionary action zone
(PAZ) This is a predesignated area around a
facility, where urgent protective action has been preplanned and will be
implemented immediately upon declaration of a general emergency. The goal is
to substantially reduce the risk of severe deterministic health effects by
taking protective action within this zone before
or shortly after a release. Urgent protective action
planning zone (UPZ) This is a predesignated area around a
facility where preparations are
made to promptly implement urgent protective action based on environmental
monitoring data and assessment of facility conditions, the goal being to avert
doses specified in international standards. Food
restriction planning radius (FRR) This is the area where preparations for
effective implementation of protective actions to reduce the risk of
stochastic health effects from the ingestion of locally grown food should be
developed in advance. In general, protective actions such as relocation, food
restrictions and agricultural countermeasures will be based on environmental
monitoring and food sampling. These zones should be roughly circular areas around the facility, their boundaries defined by local landmarks (e.g. roads or rivers) to allow easy identification during a response . It is important to note that the zones do not stop at national borders. The size of the zones can be determined by an analysis of the potential consequences. Previous studies also provide a basis for generic zone sizes for nuclear power reactor: PAZ 3-
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